Modern science has discovered that in the places where two different seas meet, there is a barrier between them. This barrier divides the two seas so that each sea has its own temperature, salinity, and density (Principles of Oceanography, Davis R., 1972, p.92).

For example, the Mediterranean sea water is warm, saline, and less dense, compared to the Atlantic ocean water. As Mediterranean sea water enters the Atlantic over the Gibraltar sill, it moves several hundred kilometres into the Atlantic at a depth of about 1000 metres with its own warm, saline, and less dense characteristics. The Mediterranean water stabilises at this depth.

The Mediterranean sea water as it enters the Atlantic over the Gibraltar sill with its own warm, saline, and less dense characteristics, because of the barrier that distinguishes between them. Temperatures are in degrees Celsius (C°). (Marine Geology, Kuenen, p. 43, with a slight enhancement.)

Although there are large waves, strong currents, and tides in these seas, they do not mix or transgress this barrier. The Quran mentions the existence of a barrier between two seas that meet and which they do not transgress. God said, in the Quran:

"He has let loose the two seas meeting together. Between them is a barrier which none of them can transgress." (The Quran - Ar-Rahman 55:19-20)

In another verse when God speaks about the divider between fresh and salt water, He mentions the existence of "a forbidding partition" with the barrier:

"He is the One who has let free the two bodies of flowing water, one sweet and palatable, and the other salty and bitter. And He has made between them a barrier and a forbidding partition." (The Quran - Al-Furqan 25:53)

In the above verse the Quran refers to the existence of a barrier which prevents the mixing of fresh water when it meets sea water. One may ask, why did God mention the partition when speaking about the divider between fresh and salt water, but did not mention it when speaking about the divider between the two seas?

Modern science has discovered that in estuaries (e.g. Nile, Tigris, Euphrates) where fresh (sweet) and salt water meet, the situation is somewhat different from what is found in places where two seas meet. It is now known that the mixing of the fresh with the salty water only occurs very far out at sea.

It has also been discovered that in estuaries, between the fresh and salt water, there exists a "pycnocline zone with a marked density discontinuity separating the two layers" (Oceanography, Gross M., 1993, p.242. Introductory Oceanography, Thurman, H., 1988, p.300). This partition (zone of separation) has a different salinity from the fresh and salt water.

Longitudinal section showing salinity (parts per thousand ‰) in an estuary. We can see here the partition (zone of separation) between the fresh and the salt water. (Introductory Oceanography, Thurman, p. 301, with a slight enhancement.)

This information has been discovered only recently, using modern instruments to measure temperature, salinity, density, oxygen solubility etc. The human eye cannot see the difference between the two seas that meet, rather the two seas appear to us as one homogeneous sea. Likewise, the human eye cannot see the division of water in estuaries into the three kinds: the fresh water, the salt water, and the partition (zone of separation). As we have seen God revealed this phenomenon in the Quran over 1400 years ago.

DEEP SEAS AND INTERNAL WAVES

Another phenomenon discovered recently is the darkness that exists in the depths of the deep oceans. Man has only recently been able to dive to these great depths aided by submersibles and submarines. It has been found that at depths of greater than 200 metres there is complete darkness and cold.

It is known that white Sun light is made up of several basic colours which can be split up to produce a spectrum. A good example of this is rain dispersing the Sun light into its component colours, causing the rainbow effect. As a ray of light reaches the ocean surface some of it is reflected while the rest is absorbed. The absorption of light by the sea is known to take place in stages. The first component of white light to be absorbed is the red wavelength at 10 metres, followed by orange (30m), yellow (50m), green (100m), violet (120m), and finally blue at depths greater than 200m. This differential absorption of light results in the ocean getting progressively darker in layers of light. Below a depth of 1000m there is no light at all (Oceans, Elder and Paernetta, 1991, p.27).

Between 3 and 30 percent of the sunlight is reflected at the sea surface. Then almost all of the seven colors of the light spectrum are absorbed one after another in the first 200 metres, except the blue light. (Oceans, Elder and Pernetta, p. 27.)

Before man was able to go to these great depths, God revealed this phenomenon in the Quran:

"Or (the unbelievers' state) is like the darkness in a deep sea. It is covered by waves, above which are waves, above which are clouds. Darknesses, one above another. If a man stretches out his hand, he cannot see it..." (The Quran - Nur 24:40)

God mentions "darknesses, one above another" and "If a man stretches out his hand, he cannot see it...", in this verse. This would refer to the phenomenon of the ocean getting progressively darker in layers of light and the fact that there is complete darkness in the ocean depths. The verse is all the more remarkable considering that human beings cannot survive unaided in the deep dark part of the oceans and need submarines or other special equipment to dive below a depth of 40m.

We can also understand from the following sentences in the previous verse, "...in a deep sea. It is covered by waves, above which are waves, above which are clouds..." that the deep waters of seas and oceans are covered by waves, and above these waves are other waves.

It is clear that the second sets of waves are the surface waves that we see, because the verse mentions that above the second waves there are clouds, but what about the first waves? Scientists have recently discovered that there are internal waves which "occur on density interfaces between layers of different densities." (Oceanography, Gross, p.205).

Internal waves at interface between two layers of water of different densities. One is dense (the lower one), the other one is less dense (the upper one). (Oceanography, Gross, p. 204.)

The internal waves cover the deep waters of seas and oceans because the deep waters have a greater density than the waters above them. Internal waves act just like surface waves, but they cannot be seen by the human eye. However, they can be detected by studying temperature or salinity changes at a given location (Oceanography, Gross, p.205).

In view of the state of knowledge in Messenger Muhammad's (PBUH) day, it is inconceivable that many of the statements in the Quran which are connected with science could have been the work of a man. It is legitimate, therefore, to award the Quran a special place on account of the guarantee of authenticity it provides and the presence in it of scientific statements which, when studied today, appear as a challenge to human explanation.